Melanocyte-stimulating hormone structure

The chief hormones of the iteurohypophysis are the polypeptides oxytocin and vasopressin. The hormone characteristic of the pars intermedia Is the melanocyte-stimulating hormone. It is usually spoken of in the plural, since in most mammals both alpha and beta forms are known. The structures of the liist two arc shown In the Table I. The most prominent effect of oxytocin is the contraction ot smooth muscle, especially of the uterus, It also has a major effect upon the muscles about ihe breast, and so stimulates the ejection of milk in I,totaling animals. It has a delinile stimulating effect upon (he muscles of Ihe ureter, urinary bladder, intestine, and gall bladder. 

Cushing disease A specific form of Cushing syndrome, which is caused by an ACTH-secreting pituitary adenoma represents approximately 66 percent of all cases of Cushing syndrome. Because of structural similarities with melanocyte-stimulating hormone (MSH), excess ACTH from pituitary adenomas can induce dermal hyperpigmentation. 

M. Afshar, R. E. Hubbard, J. E. Wikberg. Modeling of the three-dimensional structure of the human melanocortin 1 receptor, using an automated method and docking of a rigid cyclic melanocyte-stimulating hormone core peptide. J Mol Graph Model. 1997, 15, 307-317, 334. 

The melanocyte-stimulating hormones are relatively small polypeptide chains found in the neurohypophysis. The two groups (a and P) of melanocyte-stimulating hormones differ essentially by the length of the polypeptide chain. MSH has been prepared from pig, beef, horse, monkey, and human pituitary. Fractionation of the extract produces the three active polypeptides a-MSH, j8-MSH, and corticotropin. Both a- and j5-MSH are found in all animals. There is no species variation in the amino acid sequence of the a-MSH. In contrast, a small species variation exists in the structure of jS-MSH as indicated in Table 8-6. All known MSH s including corticotropin have a common denominator a heptapeptide composed of methionine. 

Melanocyte Stimulating Hormone, MSH - Shapiro et al. have studied MSH activities in a variety of vertebrate species, comparing these to known oi-and p-MSH s, and have concluded on the basis of gel filtration behavior, radioimmunlogical assays and bioassays that the structures of the major MSH hormones in several of the species are diffgjent from those which have been characterized previously. Sandman et al. ment of MSH in the passive avoidance response. 

Other Pituitary Hormones.-Continuing research on melanocyte-stimulating hormone (MSH) has been well-summarized in three 1967 reviews Some new structure-activity relationships have been reported on synthetic C-terminal decapeptides related to 8-MSH of several species. The total synthesis of monkey 8-MSH was reported A radioimmunoassay was developed for 8-MSH and claimed to be capable of distinguishing 8-MSH from a-MSH and ACTH. 3-MSH was found to protect rats exposed to ole-body x-lrradl-... 

The weakness of proteinoid function is plausible from a viewpoint of molecular evolution, and from a chemical standpoint it is due to the primitive structure of proteinoid showing a relatively simple, or an elementary, reaction such as the active site of enzyme. For example, the melanocyte stimulating activity of the proteinoid is close to the activity of the active site peptide of the hormone, MSH. 

Lack of negative feedbtick of cortisol on the anterior pituitary results in an excessive secretion of ACTH. The structure of this hormone contains part of the amino acid sequence of melanocyte-stimulating homione. Where excessive ACTU secretion occurs, patients may show darkening of the skin and mucous membranes. 

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